The possibility that tumor-specific enzyme/isoenzyme changes exist in leukemic cells is being explored in this research proposal by studying the enzyme acivities and isoenzyme profiles of hexosaminidase, ppyrovate kinase and isocitric dehydrogenase in the lymphoblasts of children with ALL. All 3 enzymes under study were selected because they have isoenzyme forms coded for on chromosome 15; thus the pattern of changes found may provide clues to the nature of the leukemia transformation process(es). Serial followup of patients and comparison to values obtained with normal resting lymphocytes and normal lymphocytes induced to undergo blastogenesis are being used to determine the leukemia-specificity and, therefore, the clinical usefulness as tumor markers, of any differences discovered.